RU2753838C1 - Method for determining the distance to ground fault locations on two power transmission lines in networks with low ground fault currents - Google Patents

Abstract

FIELD: electric power industry.

SUBSTANCE: invention relates to the electric power industry; it can be used to determine locations of damage in earth faults on two different power transmission lines of a 6-35 kV distribution network with low earth fault currents. In the claimed method, phase current and phase voltage are measured, according to the increase in phase currents of damaged phases on one and the other line, the emergency mode associated with the occurrence of single-phase earth faults on two lines, at different phases, is determined. According to the method, along with currents and voltages of the emergency mode, currents and voltages of the pre-emergency (normal) mode are recorded, components of the pure emergency mode are obtained from the difference of currents and voltages of the emergency and pre-emergency modes, distances to locations of damages on one and the other lines are calculated, ensuring a reduction in the influence of the current distribution of branches and the load mode on the accuracy of calculations due to the use of currents and voltages of the pure emergency mode.

EFFECT: technical result is an increase in the accuracy of the method for determining the distance to locations of earth faults.

1 cl, 5 dwg

Description

The invention relates to the electric power industry and can be used to determine the locations of damage during ground faults on two different power lines of the 6-35 kV distribution network with low ground fault currents.

The known "Method for determining the distance to ground faults on two power lines in networks with low ground fault currents" (RF Patent No. 2557375 dated 04/29/2014, IPC G01R 31/08, publ. 07/20/2015, Bul. No. 20), according to which the phase current and phase voltage are measured using a resistance measuring organ. The resistance measuring organ is switched on to the phase currents and phase voltages of damaged lines extending from some substation buses, according to the growth of phase currents I _f1 and I _{f2 of} damaged phases f1 on one line and f2 on another line, determine the occurrence of single-phase earth faults on two lines, at different phases, the absolute values of the inductive resistance X _f1 and X _{f2 of the} contours of the damaged phases f1, f2 are calculated according to the following expressions:

and calculate the distance to the place of damage l _1k on one line and the distance to the place of damage l _2k on the other line according to the formulas

where Re (U _{f1 (2)} ), Im (U _{f1 (2)} ), Re (I _{f1 (2)} ), Im (I _{f1 (2)} ) - real and imaginary components of the phase current and voltage of the damaged phases, X _{0 lud} , X _1lud - specific inductive resistances of direct and zero sequence power lines.

The disadvantage of this method is the low accuracy associated with incomplete consideration of the mutual inductances of the phases, the magnitude of the load and branches when determining the distance to places of damage to power lines.

The closest technical solution is "A method for determining the distance to ground fault locations on two power lines in networks with low ground fault currents" (RF Patent No. 2674528 of 12/20/2017, IPC G01R 31/08, publ. 12/11/2018 , Bull. No. 35), according to which the phase current and phase voltage are measured using a resistance measuring organ, the resistance measuring organ is switched on to the phase currents and phase voltages of damaged lines extending from some substation buses, according to the growth of phase currents I _f1 and I _f2 damaged phases f1 on one line and f2 on the other line, determine the occurrence of single-phase ground faults on two lines, on different phases, calculate the absolute values of the inductive resistance X _f1 and X _{f2 of the} contours of the damaged phases f1, f2 according to the following expressions:

where Re ( U _{f1 (2)} ), Im ( U _{f1 (2)} ), Re ( I _{f1 (2)} ), Im ( I _{f1 (2)} ) - real and imaginary components of the phase current and voltage of the damaged phases, calculate the distance to the place of damage l _{1 k} on one line and the distance to the place of damage l _{2 k} on the other line. When determining the distance to the places of double earth faults, the mutual inductive resistances of the phases of the damaged power transmission lines are additionally taken into account, and the calculation of the distance to the nearest place of damage l _1k and the distant place of damage l _{2k is} carried out according to the following expressions:

;

– сопротивления взаимной индукции неповрежденных фаз первой линии относительно поврежденной фазы;

;

– сопротивления взаимной индукции неповрежденных фаз второй линии относительно поврежденной фазы; I _ф11 – ток поврежденной фазы первой линии; I _ф22 - ток поврежденной фазы второй линии; I _ф12, I _ф13 – токи неповрежденных фаз первой линии; I _ф21, I _ф23 – токи неповрежденных фаз второй линии; х _л1, х _л2 – удельные индуктивные сопротивления соответственно первой и второй линии электропередачи; z _m1, z _m2 – удельные сопротивления взаимной индукции соответственно первой и второй линии электропередачи.where

;

- resistance of mutual induction of undamaged phases of the first line relative to the damaged phase;

;

- resistance of mutual induction of undamaged phases of the second line relative to the damaged phase; I _f11 - current of the damaged phase of the first line; I _f22 - current of the damaged phase of the second line; I _f12 , I _f13 - currents of undamaged phases of the first line; I _f21 , I _f23 - currents of undamaged phases of the second line; x _l1 , x _l2 - specific inductive resistances of the first and second power transmission lines, respectively; z _m1 , z _m2 - specific resistances of mutual induction, respectively, of the first and second power transmission lines.

The disadvantage of this method is the low accuracy associated with incomplete taking into account the magnitude of the load and the influence of the branches when determining the distance to the places of damage to power lines.

The objective of the invention is to improve the accuracy of the method for determining the distance to ground faults on two power lines in networks with low ground fault currents by reducing the influence of the load and branches of the power lines.

The task is achieved by the method of determining the distance to the places of earth faults on two power lines in networks with low earth fault currents, according to which the phase current and phase voltage are measured using a resistance measuring organ, the resistance measuring organ is switched on to the phase currents and phase voltages of the damaged lines departing from some substation buses, according to the growth of the phase currents of the damaged phases on one and the other line, determine the emergency mode associated with the occurrence of single-phase ground faults on two lines, on different phases, calculate the distance to the fault location on one line and the distance to the place damage on another line. According to the proposal, along with the currents and voltages of the emergency mode, the currents and voltages of the pre-emergency (normal) mode are recorded, the components of the purely emergency mode are obtained from the difference between the currents and voltages of the emergency and pre-emergency modes, the distances to the fault locations on one and the other lines are calculated, ensuring a decrease in the influence of the current distribution of the branches and load mode on the accuracy of calculations due to the use of currents and voltages of the purely emergency mode, according to the following expression:

,

,

- расстояние до места повреждения;

– удельное сопротивление взаимной индукции;

– удельное сопротивление линии;

– фазное напряжение соответствующего режима на шинах;

– ток, протекающий в месте установки защиты;

– ток, протекающий в месте повреждения; индекс «x» обозначает анализируемую линию (L1 – соответствует линии 1, L2 – линии 2); индекс «y» указывает фазу (пов.1 – поврежденная фаза анализируемой линии, пов.2 – поврежденная фаза соседней линии, неп – неповрежденная фаза); индекс «z» соответствует расчетному режиму (н – нормальный режим, кз – аварийный режим, ав – чистоаварийный режим).where

- distance to the place of damage;

- specific resistance of mutual induction;

- line resistivity;

- phase voltage of the corresponding mode on the buses;

- current flowing in the place of protection installation;

- current flowing at the place of damage; index "x»Denotes the analyzed line (L1 - corresponds to line 1,L2 - lines 2); index "y»Indicates the phase (st.1 - damaged phase of the analyzed line, st.2 - damaged phase of the adjacent line, undamaged phase); index "z»Corresponds to the design mode (n - normal mode, kz - emergency mode, aw - purely emergency mode).

FIG. 1 is a diagram illustrating the application of the overlay method.

FIG. 2 shows an equivalent circuit for a purely emergency mode in a three-phase version, which explains the calculated ratios for the proposed method. FIG. 2 introduced the following notation:

z _with - equivalent three-phase resistance of the system - (1);

z _l - three-phase line resistance - (2);

R _p1 , R _p2 - transition resistances at the points of closures (3 ₁ ) and (3 ₂ ) on the first and second lines;

z _n1 - equivalent three-phase load resistance of the first line (4₁);

z _n2 - equivalent three-phase load resistance of the second line (4₂);

IO - measuring organ of resistance of the first (5 ₁ ) and second (5 ₂ ) power lines.

l ₁ , l ₂ - distances to ground faults on the first and second power lines;

L ₁ and L ₂ - the length of the first and second transmission lines.

FIG. 3 shows a diagram of a section of an electrical network for carrying out simulation experiments.

FIG. 4 illustrates the dependence of the calculated distances to the points of damage on the actual ones for double earth faults on power lines without branches (Fig.4a - for point k 1 (Fig. 3); Fig. 4.b - for point k 2 (Fig. 3 )).

FIG. 5 illustrates the dependence of the calculated distances to the points of damage from the actual ones for double earth faults on power lines with branches (Fig. 5.a - for point k 3 (Fig. 3); Fig. 5.b - for point k 4 (Fig. 3 )).

The proposed method is implemented as follows.

As in the prototype method, in the proposed method for determining the distance to ground faults on two power lines in networks with low ground fault currents by the growth of phase currents of damaged phases on one line and on the other line, the occurrence of single-phase ground faults on two lines is determined. lines at different phases.

Known methods for determining the distance to ground fault locations on two power lines in networks with low ground fault currents (for example, a prototype method) are based on the measurement and further processing of emergency mode parameters. The emergency components of currents and voltages contain components of purely emergency and pre-emergency (normal) modes. It is advisable to divide the emergency mode into the load (pre-emergency) and purely emergency components using the superposition method. Note that the purely emergency components of currents and voltages are formed by subtracting from the components of the emergency mode, the components of the previous normal (pre-emergency) mode.

The main idea of the superposition method is to equalize the number of branches in the electrical network before and after damage. This implies the preparation of two equivalent circuits for a section of the electrical network for normal and emergency modes. The equivalent circuit for double earth faults on two lines without taps is shown in FIG. 1.

When drawing up the equivalent circuit for the normal mode, a fictitious EMF branch is switched on at the place of the alleged short circuit, the value of which is equal to the pre-emergency voltage at the place of damage (Fig. 1.a). The equivalent circuit of the emergency mode, on the contrary, does not contain EMF at the place of the alleged short circuit (Fig. 1.b). Subtracting, according to Kirchhoff's laws, from the equations of the emergency scheme, the equations of the pre-emergency mode, we obtain a purely emergency scheme (Fig. 1.c), which contains in an undistorted form all the necessary information to determine the location of damage.

Calculated expressions for determining the distance to the places of damage will be obtained from the equivalent circuit for a purely emergency mode in a three-phase version (Fig. 2).

Pre-emergency stresses at the site of damage (Fig. 2) are determined by the expression:

- расстояние до места повреждения;

– удельное сопротивление взаимной индукции;

– удельное сопротивление линии;

– фазное напряжение соответствующего режима в месте установки защиты;

– ток, протекающий в месте установки защиты;

– ток, протекающий в месте повреждения; индекс «x» обозначает анализируемую линию (L1 – соответствует линии 1, L2 – линии 2); индекс «y» указывает фазу (пов.1 – поврежденная фаза анализируемой линии, пов.2 – поврежденная фаза соседней линии, неп – неповрежденная фаза); индекс «z» соответствует расчетному режиму (н – нормальный режим, кз – аварийный режим, ав – чистоаварийный режим),

– доаварийное напряжение в месте повреждения.In expression (1) and further, the following designations are introduced:

- distance to the place of damage;

- specific resistance of mutual induction;

- line resistivity;

- phase voltage of the corresponding mode at the place of protection installation;

- current flowing in the place of protection installation;

- current flowing at the place of damage; index "x»Denotes the analyzed line (L1 - corresponds to line 1,L2 - lines 2); index "y»Indicates the phase (st.1 - damaged phase of the analyzed line, st.2 - damaged phase of the adjacent line, undamaged phase); index "z»Corresponds to the design mode (n - normal mode, kz - emergency mode, aw - purely emergency mode),

- pre-emergency voltage at the place of damage.

In the case of using a purely emergency circuit (Fig. 2), the effect of the load component is reduced. In case of short circuits at points k 1 and k 2 (Fig. 2), the EMF at the place of damage is determined by the following expression:

равна доаварийному значению

, тогда, подставив выражение (1) в уравнение (2), получаем следующее соотношение: In accordance with the superposition method, EMF at the place of damage

equal to pre-emergency value

, then, substituting expression (1) into equation (2), we obtain the following relation:

After removing the common factors from the brackets, we have the following equality:

Expressing l _x from expression (4), we obtain the formula for calculating the distance to the damage site:

or

. Аналогичным образом снижается влияние на точность расчета расстояний до повреждений ответвлений ЛЭП.The use of a purely emergency mode reduces the effect of the load on the accuracy of calculating the distances to damage, taking into account the fact that the current flowing through the load is the same both in the load and emergency modes, therefore the value

... In a similar way, the impact on the accuracy of calculating the distances to damage to power line branches is reduced.

Since the transient resistance, as a rule, is assumed to be active, its influence can be excluded by considering only the reactive components.

Then the distance to the point of damage is determined by the following expression:

Expression (7) is universal and allows you to determine the distance for both the near and far points of damage to power lines in case of double earth faults.

Measurement of currents and voltages of the normal (pre-emergency) and emergency process is carried out at the installation site of the IO 5 ₁ and 5 ₂ , (Fig. 2) connected to the phase current and phase voltage relative to the ground.

Practical implementation of the proposed method for determining the distance to ground fault locations on two power lines in networks with low ground fault currents can be performed using resistance measuring devices (5 ₁ and 5 ₂ ), which are part of modern distance protection systems. The resistance measuring element, connected to the phase current and phase voltage, meets the requirement of proportionality of the resistance at the relay terminals to the distance to the fault location in the double earth fault mode in a distribution network with low earth fault currents. Note that obtaining the purely emergency components of currents and voltages necessary for calculating the distances to damage sites according to expression (7) is realized by subtracting from the components of the emergency mode, the components of the previous normal (pre-emergency) mode. Information about the pre-emergency components of currents and voltages is updated for each current measurement cycle in the memory of a device that implements the proposed method.

The assessment of the accuracy of the proposed method for determining the distance to ground fault locations on two power lines in networks with low ground fault currents was implemented in the Matlab software package and the Simulink simulation environment. Damage simulation was carried out on a model of a section of an electrical network containing a power transmission line with distributed parameters and assuming a given set of configurations (Fig. 3).

Ом/км; удельное сопротивление взаимной индукции

Ом/км; переходные сопротивления в местах замыканий определялись случайной величиной, распределенной по равномерному закону в диапазоне от 0 до 20 Ом; потребляемая мощность нагрузки принята одинаковой для всех присоединений:

, что соответствует сопротивлению

The parameters of the simulation model included: network voltage 35 kV; line lengths: L ₁ = 20 km; L ₂ = 20 km; L ₃ = 25 km; L _4.1 = 10 km; L _4.1 = 5 km; L _4.2 = 10 km; L ₅ = 30 km; L _6.1 = 20 km; L _6.2 = 10 km; resistivity of each phase

Ohm / km; specific resistance of mutual induction

Ohm / km; the transient resistances at the points of short-circuits were determined by a random value distributed according to a uniform law in the range from 0 to 20 ohms; power consumption of the load is assumed to be the same for all connections:

, which corresponds to the resistance

During the simulation, the following assumptions were made:

1) the three-phase elements of the system were assumed to be symmetrical;

2) the transition resistance is chosen to be purely active;

3) the type of damage and the damaged phases are known.

The processing of the simulation results made it possible to obtain the dependence of the calculated distances on the actual values set during the simulation experiments (Fig. 4, Fig. 5). To analyze the advantages of the proposed method for determining the distance to ground fault locations on two power lines in networks with low ground fault currents, the results of calculating the distances to the fault locations were compared with the values calculated by the prototype method using emergency mode parameters.

FIG. 4 shows the calculated dependences for double earth faults on lines without branches, obtained using a purely emergency scheme (circle on the graph), and according to the parameters of the emergency mode corresponding to the prototype method (cross on the graph) for points k 1 and k 2 (Fig. 3). An analysis of the results obtained shows that the use of a purely emergency mode can significantly reduce the deviation of the calculated distances from the actual ones. Compared with the prototype method, the proposed method for determining the location of damage can reduce the maximum value of the relative error from 45% to 16%.

To substantiate the advantages of using the developed method for determining the distance to ground faults for lines with branches, a double ground fault was simulated at point k 3 (short circuit before branch) and at point k 4 (short circuit after branch) (Fig. 3).

The calculated values of the prototype method in the presence of power line branches have a relative error reaching 50%, and are indicated by circles in FIG. 5. The use of a purely emergency mode in the proposed method allows to reduce the maximum value of the relative error in calculating the distance to the place of damage to 15% (Fig. 5). Reducing the size of errors is achieved by reducing the influence of current distribution on lines with branches, as well as the load component when introducing a purely emergency mode.

Thus, the proposed method allows you to accurately determine the distance to ground fault locations on two power lines in networks with low ground-fault currents by reducing the influence of the current distribution of power lines with branches and the load mode. The results of simulation modeling of a 35 kV electrical network section showed a significant (more than three times) reduction in the error in calculating the distance to the fault location and a corresponding reduction in the transmission line bypass zone in case of double ground faults.

Claims (3)

A method for determining the distance to ground fault locations on two power lines in networks with low ground fault currents, according to which the phase current and phase voltage are measured using a resistance measuring organ, the resistance measuring organ is switched on to the phase currents and phase voltages of damaged outgoing lines from some substation buses, according to the growth of the phase currents of the damaged phases on one and the other line, the emergency mode associated with the occurrence of single-phase ground faults on two lines, on different phases is determined, the distance to the fault location on one line and the distance to the fault location on the other are calculated lines, characterized in that, along with the currents and voltages of the emergency mode, the currents and voltages of the pre-emergency (normal) mode are recorded, the components of the purely emergency mode are obtained from the difference between the currents and voltages of the emergency and reduction of the influence of the current distribution of the branches and the load mode on the accuracy of calculations due to the use of currents and voltages of the purely emergency mode, according to the following expression

where

- distance to the place of damage;

- specific resistance of mutual induction;

- line resistivity;

- phase voltage of the corresponding mode on the buses;

- current flowing in the place of protection installation; - index "x»Denotes the analyzed line (L1 - corresponds to line 1,L2 - lines 2); index "y»Indicates the phase (st.1 - damaged phase of the analyzed line, st.2 - damaged phase of the adjacent line, undamaged phase); index "z»Corresponds to the design mode (n - normal mode, kz - emergency mode, aw - purely emergency mode).

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